LIGHTING UP A NEW YEAR

For the end of my month mostly-not-off, I finally let myself waste 
New Year's Eve and Day on something completely pointless - the 
optical communication experiments I didn't get reading in time for 
ROOPHLOCH, as mentioned in 2024-10-01ROOflop.txt. As a result this 
post will hopefully be transmitted by light before being received 
and automatically uploaded to aussies.space. Actually it's being 
sent and received by the same computer at the moment, which is 
rather pointless, but it makes it easier to debug.

It's all still just a bird's nest of breadboards on my workbench. I 
was hoping to start on the cases for the transmitter and receiver 
today, but somewhat predictably got bogged down for hours trying to 
get the software configuration right. Most things worked quite 
easily, but I wasn't getting the EOF character to terminate 'cat' 
at the end of the file, whereafter the file gets automatically 
uploaded to aussies.space by the receiver computer. The description 
in the stty man page really doesn't suggest it, but by trial and 
error I eventually discovered that enabling the 'icanon' setting 
lets the EOF character (default Ctrl-D) through without messing 
other things up.

With that sorted out I experimented with baud rates, and far from 
pushing the limits at 200 baud I can get up to 4800 baud over the 
short distance of my test rig. Since I'm aiming for sensitivity 
rather than bandwidth that's far more than sufficient. So I set to 
writing up some transmit and receive scripts to use to post to the 
phlog. Even though the stty documentation caught me out, I do think 
it's wonderful how short the shell scripts to do this can be:

optictx.sh
------------------------------------------------------------------
#!/bin/sh
# optictx.sh [file] [serial device] [baud rate]
# eg. optictx.sh hello.txt /dev/usb/ttyUSB0 4800

FILE="$1"
DEV="$2"
[ $3 ] && BAUD=$3 || BAUD=200

stty -F $DEV raw icanon -crtscts -echo $BAUD || exit
echo "  Transmitting $FILE at $BAUD baud..."
cat "$1" > $DEV
echo -e '\x04' > $DEV
------------------------------------------------------------------

opticrx.sh
------------------------------------------------------------------
#!/bin/sh
# opticrx.sh [filename] [serial device] [baud rate]
# eg. opticrx.sh hello.txt /dev/usb/ttyUSB0 4800

FILE="$1"
DEV="$2"
[ $3 ] && BAUD=$3 || BAUD=200
HOST=ausshell
DEST=/home/freet/goph/phlog
CMD="cd /home/freet/goph/phlog && /home/freet/bin/simplemkphlog.sh"

stty -F $DEV raw icanon -crtscts -echo $BAUD || exit

echo "  Receiving $FILE at $BAUD baud..."
cat $DEV > "/tmp/opticrx_$FILE"

echo "  Uploading..."
pscp -C -sftp "/tmp/opticrx_$FILE" "$HOST:$DEST/$FILE"
plink -C -batch "$HOST" "$CMD"

echo "  Operation Complete"
rm "/tmp/opticrx_$FILE"
------------------------------------------------------------------

A photo of my test set-up, transmitting a pretty modest 47cm 
distance from red LED array to photodiode lens, but I'm sure it can 
go much further:
gopher://aussies.space/I/~freet/photos/optical_comms/bench_test.jpg

See the 2024-10-01ROOflop.txt for the circuits. I forgot to include 
the pull-down resistor on the output to the RS232 TTL adapter from 
the receiver board, which I've added there now, but otherwise 
nothing's changed.

Soldering up the boards properly should be easy, but the cases are 
going to be tricky to work out because they have to fit on top of 
my tripods. Maybe I'll get to that on the weekend. Best not put it 
off and accidentally let yet another ten months pass me by before 
ROOPHLOCH 2025. Still tonight it will be shifted aside yet again to 
make way for tomorrow's work, hopefully after successfully sending 
this.

In other news, not so much doof-doof music from the festival this 
year, it seems. Maybe that style's on its way out? Only those lower 
pitch sounds carry this far so it mostly seemed quieter this year. 
They had a fireworks display which I went outside to watch but it 
was more of a colourful glow at this distance, even through my 
wonky highest-magnification binoculars. Just as the display ended 
the faint sound of the new year's countdown reached me, delayed by 
the distance.

I didn't get around to buying booze for my permitted single day of 
alcohol consumption in 2024 (any day, but only once per year), 
having finally exhausted stocks. But in a way my apathy there is 
exactly the intended result of my rule.

Alright, let's see if this works...

Nope, stty is still confusing me. Adding '-echo'...

 - The Free Thinker